Тhere are add-ons that are installed directly through the Gmail service!

In March, Google promised to create a single internal space in which it will be possible to find all the add-ons for Gmail. Earlier plug-ins had to be installed separately from different sources. Now they are available through a special menu of mail service.

You can add an add-on from your computer and it will become active on all your devices.
There are not many plug-ins now and they are intended for business users. There is the addition of Trello, for example, which allows you to quickly create cards on the boards, without leaving the mail. Also they promise to add a service for signing DocuSign documents soon.

Add-ons works now in browsers only and on Android devices. Later, the innovation will be available to iOS users, but it is unknown when exactly.

Users say that Google adds some useless features, but they don’t do simple innovations for many years. It would be better to make the "viewing area" by default, not from the laboratory.